The force said it has “strong plans” in place involving a significant number of officers to deal with the planned Extinction Rebellion (XR) action on Good Friday.

The airport said it is “working with the authorities” to address the threat of mass disruption, while Home Secretary Sajid Javid has urged police to use the “full force of the law”.

Metropolitan Police Assistant Commissioner Nick Ephgrave said the protests were “increasing in intensity” and warned demonstrators against targeting Heathrow Airport.

He told the Press Association: “Protesters can expect a robust police response. We are determined to keep the airport operating.”

A Met statement added: “The airport is part of our national infrastructure and we will not allow the illegal activities of protesters to cause further disruption and misery to thousands of travellers, many of them families, over Easter.

“We would urge any protester planning to attend Heathrow to strongly reconsider.”

The Met have arrested more than 500 protesters as illegal demonstrations continue at Waterloo Bridge, Oxford Circus and Parliament Square, while demonstrations are allowed to continue only at Marble Arch.

The arrests are for obstructing the highway and breaching the Section 14 order that prohibits protests apart from at Marble Arch, and 10 people have been charged with those offences.

A further three people who have been charged by British Transport Police appeared in court on Thursday morning.

A spokesman for the XR group said activists will be staging protest action at Heathrow on Friday, with around 500,000 people expected to fly out for Easter breaks over the bank holiday weekend.

Speaking after a briefing with Metropolitan Police Commissioner Cressida Dick on Thursday, the Home Secretary said she had told him that more than 1,000 officers were being deployed to the streets of the capital each day of the protests.

“Let me be clear – I totally condemn any protesters who are stepping outside the boundaries of the law,” Mr Javid said.

“They have no right to cause misery for the millions of people who are trying to lead their daily lives. Unlawful behaviour will not be tolerated.

“I expect the police to take a firm stance and use the full force of the law.”

Climate activists surround a pink boat that has been parked during an Extinction Rebellion demonstration at Oxford Circus (Yui Mok/PA)

Scotland Yard said officers have been asked to work 12-hour shifts, while rest days and leave has been cancelled.

The force said that although the Violent Crime Task Force (VCTF) has been ring-fenced, the protests are diverting officers away from their local duties.

London Mayor Sadiq Khan has written a letter to the Home Secretary about the increasing cost of policing a growing number of protests in London, and he is working with the Met to consider making a special grant claim over the current demonstrations.

A climate activist is led away by police officers from an Extinction Rebellion demonstration at Oxford Circus (Yui Mok/PA)

The fourth day of protests – which have seen activists glue themselves to public transport and block bridges and major roads across the capital – began with a challenge to Environment Secretary Michael Gove to meet with activists at Parliament Square to find a solution to the issue.

And organisers said they expected even more people to join the protests, with a statement – which was later deleted – adding: “Easter weekend is tomorrow and thousands more rebels will join.

“Police struggle to arrest 350 and there are 10 times that number prepared to be arrested.

“The hollowed-out British state is overwhelmed.”

Cathy Eastburn, 51, Mark Ovland, 35, and Luke Watson, 29, were remanded in custody after they were charged over their alleged involvement in obstructing trains at Canary Wharf station on Wednesday morning.

All three indicated a not guilty plea when they appeared at Highbury Corner Magistrates’ Court.

Speaking from Waterloo Bridge, Dr Gail Bradbrook, a co-founder of the XR group, said demonstrators would continue to act despite the first people being charged over the disruption.

“It (the charges) might put some people off and we escalated our strategy by focusing on the rail infrastructure,” she told the Press Association.

“It’s certainly an option that tactics will be escalated if our demands are not met,” she said.

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